Katrina was bad, but I'd estimate that the Everstorm would be significantly worse.
The Shin live in a part of Roshar rather protected from Highstorms due to their topography and the fact the storm has to travel over land for a long time. This always will make any storm weaker.
The Everstorm however, would slam into Shinovar in a devastating fashion after acquiring significant moisture from the Endless Ocean (especially if comes from the north-west). As we know, the northern climes of Roshar seem to be WARMER than the southern climes (the Frostlands are on the southern side of the continent and the tropical Reshi Island on the north) so if we assume the Everstorm strengthens/recharges over warm open water like regular storms this will be a huge storm when it hits Shinovar. Shinovar's only saving grace may be if the mountains on its western side are significantly large enough to pull most of the moisture out of the air as it rise over the peaks, creating a rain-shadow effect. I doubt this would be enough. Now, if the storm comes from a more northern direction than western, it could hit Shinovar through the bay it shares with Iri. If this were to happen destruction would be vast.
The last thing to consider: architecture. The architecture of Shinovar has probably never been developed to deal with strong storms. Let alone any coming from the WRONG direction. As we know in mainland Roshar, a lot of buildings are built in protective laits...but they're unprotected on the western side due to the natural erosion created by the wind and rain of Highstorms. These buildings get destroyed by the Everstorm and they probably are built stronger than buildings in Shinovar in general. Thus buildings in Shinovar will be blown away, will collapse, or will generally not be soundly built to withstand this type of destruction, even if the mountains weaken the storm some.
Given all of these points, I would argue that the impact will be MUCH WORSE than Katrina. I'd liken the immediate devastation to be like the Boxing Day Tsunami of 2004. Immediate, unforeseen, and catastrophic.
[Edit: here's an old thread on a similar topic of the Everstorm and Shinovar, if you're interested in seeing the previous discussions]